Planographic printing plate



United States Patent 2,806,424 PLANOGRAPHIC PRINTING PLATE Anthony L. Ensink, Chicago, In.

, No Drawing. Original application March 27, 1947, Se-

rial No. 737,705. Divided and this application December 18, 1950,'SerialNo. 201,493

5 Claims. (Cl. 101-149.2

. vide a paper or comparable printing surface having a coating of an alignate. An object is, therefore, to provide a use for alginates in connectionwith the making of printing plates or sheets.

Another objectis to provide an alg-inate coating which may be applied to supports or surfaces of various materials. The coating of the present invention might be applied to supports formed of metal, such as steel, aluminum, copper or zinc. It might be applied to glass or composition supports. Generally a flexible support is preferable.

The invention pertains primarily to lithographic plates, and has as an important object to provide an inexpensive method of lithographic reproduction from a typed, written, drawn or otherwise inscribed grease receptive image, and which will give a large number of faithful reproductions, It is recognized that previous attempts have been made with varying degrees of success to treat paper and other supports such as zinc, aluminum, copcoating is, therefore, eilect a waterproofing coating.

Many different suitable coatings are available for this purpose. The coatings may be formed of casein, ureaformaldehyde, melamine, resins, cellulose derivatives, chlorinated rubber and varnishes. Whatever material is chosen for coating the support above referred to, it may be applied in any mannerby a coating machine such as a roll coater, a brush coater or an air blade coater. I

I With the support coated as above described and dried, it is ready to receive the alginate coating which forms the printing surface. This printing surface coating consists of a solution of sodium alginate or ammonium alginate, preferably a solution of from 2 /z% to 3%. With the alginate in solution may be included one or more fillers. Typical fillers are barium sulphate, china clays and other clays, calcium carbonate and titanium dioxide. pigments may be as-high as one part alginate to fivc part fillers of one part alginate to eight part .fillers.

The ratio of dry alginates to dry fillers or 2,806,424 Patented Sept. 17, 1957 The alginates are normally Water soluble. A suitable method for rendering them insoluble includes the step of incorporating metal salts directly into the alginate pigrnentsolution. The metal salts used in this operation are preferably aluminum chloride and zinc chloride (about /2 to 5%, based on the amount of dry alginate). Other metal salts such as calcium and iron may be used.

The alginate coating, with or without filler, may be applied first onto the Water-proofed paper base sheet and the coating subsequently treated with the metal salts for insolubilization.

The 'alginates, fillers, pigments and metal salts are applied to the support or base as a suspension in water. The \alginate solution may be applied to the support manually or otherwise. Several coats will normally be applied and each is dried before the next has been applied.

With a paper or other support suitably water-proofed and suitably coated with the alginate solution, it is ready for use. .While it may be used in a number of ways, the three following methods are those of most general importancez" (1) .The plate as prepared above may be used in what is known as a direct image printing plate. In this manner of use an image is made on the plate by typing, drawing or writing. This is done with a suitable ink or a pencil or an equivalent means. Thus one or more grease receptive areas are formed on the plate and they are predetermined by the manner in which they are formed, as by typing or drawing, etc. The plate with the image thus formed is put into an oifset printing press and by the usual oihset method a large number of copies can be made of the original impression.

Preferably before the plate is actually put on or in an offset press, it is wetted out with an etching solution. The etching solution renders water-receptive and wets those areas on the plate where no deposits of printing, drawing, writing or other images have taken place. These areas repel the ink, whereas the image written, drawnor typed on the plate is grease receptive and retains the ink.

Many suitable etching solutions are available. Among them is a gum arabic solution with barium nitrate and water. Another is an oxalic acid solution with ammonium sulphate and nitric acid in a weak solution. The invention is not limited to these particular etching solutions nor to any other etching solution. Those mentioned are referred to merely as comprising suitable etching solutions.

In using the plate, the etching solution or a dilute form of an etching solution, which is normally called the fountain solution, is kept constantly on the plate to wet it in the manner well-known in offset printing. The result of the steps and treatment above described is that the surfaceof the plate rejects greasy ink at all points except those on which printing, writing, drawing or other predetermined images have been formed.

(2) A second important use for sodium align-ate and ammonium alginate is as a light-sensitive coating which is prepared of sodium alignate or other alignates, and

This coating can be applied by V without departing from the spirit of this invention. .nPlasticizens such as glycerine, glucose, Calgcn (Sow dium hexametaphosphate), or sorbitol can be added to prevent breaking of the film of the coating, which might otherwise occur, due to its relative brittleness. One or more of such plasticizers may be included in any formula. 1 I r V The plate made :as described above and now coated with the light-sensitive formula above mentioned or. its equivalent is ready for use when :the coating is .dried. The plate :may be :put into a vacuumior other printing frame in contact with :a negative. It is then exposed to light, preferably an are light or an equally strong lig'ht source, for .alength of "time depending upon the distance of the light from the plate and the quality of the negative, and after :suitable exposure the plate is removed from the frame or other holding means and'is separated from the negative. .Developing ink, which is well-known inthe art, is applied the plate and the plate is developed out in the usual known manner. .Excess developing ,ink is removed and the plate is preferably put under running .water to remove the ink on .all areas except those which have been hardened and made insoluble by the light. The hardened and :insolubilized areas are receptive to. printing inks.

After these steps the plate, to which .the coating of hichromate sensitized alginate has been applied, is ready for use and may be put into an offset printingpress f0 making reproductions. The plate, once made as described above, may he used for a large number of reproductions;

(,3) A third important application of sodium alginate and ammonium algina-te embodies the method of using the plate above described and making that plate a photosensitive plate. The method for doing this comprises the treatment of the plate either with a sodium algi-nate solution or an ammonium alginate solution to which silver salts are added, such as silver bromide, silver chloride and silver iodide, or any combination thereof.

This coating can be applied .to the plate described above, whether that plate be formed of paper or another support or metallic support, or any of the plate supports previously mentioned in connection with the basic preparation of the plate. The formula below described will produce a photosensitive halide emulsion, the colloid of which is analginate, in place of the gelatin .or other products known in the art, such as polyvinyl alcohol and other known materials.

A suitable formula for use in making a photosensitive alginate emulsion is as follows: 250 grams of a 2% solution of sodium alginate or ammonium alginate. To this is added '18 grams of ammonium bromide and 1 gram of potassium iodide, which are dissolved in 100 grams'of water. To the combined solution of alginates and bromides the following solution is added: 30 grams of silver nitrate dissolved in 50 grams of water and 25 grams of ammonium hydroxide.

This photosensitizing coating process .must be carried out under conditions such as those prevailing in the manufacture of photosensitive products.

The plate formed with the photosensitive silver alginate is suitably. dried and is then ready for exposure, developing and fixing operations and for further use. The important feature of this 'photosensitized plate is that it can be stored for a long time without losing its qualities and being instantly ready for practical use. For actual use, the plate, together with a negative, is subjected to light of' suitable intensity, such as incandescent light. The plate, thus sensitized, may be used either for contact printing or enlargement and after a suitable exposure the usualphotographic steps of developing and fixing are carried-out and thereby the exposedsilver salts are reduced to metallic silver.

.Since, the ultimate use of the photosensitive silver alginate plate is the creating of a surface from which many reproductions can be made by lithographic printing or by other printing methods, other steps are then carried out. The reduced metallic silver now present.

4 in the developed andfixed plate is not grease receptive-.that is to say, it does not accept greasy inks. Therefore, the reduced metallic silver then converted into a chromate salt by the use of a suitable bleaching agent. This agent may comprise copper sulphate solution), potassium bromide (10% solution) and chromic acid or ammoniumbichromate (1% solution). Sample formula: 500 cc. copper sulphate solution; 500

1 cc. potassiumbromide solution; 100 ccJOfeither chromic important feature is the rendition of high fidelity reproductions obtained with this plate.

Much of the -discussion above has referred to paper However, the invention is not: limited to that support nor to a support of any particularsupports for the plate.

nature. The alg'ina-te coatings above described may be applied to metal supports or, in "fact, many-supports capable of carrying the coating and capable of use in'a printing process.

The-inventionis not limited to the use of silver and maybe embodied inthe use of many different metallic salts. Inparticular, aluminum and zinc salts may' be used, and so also may chromium salts. The invention is, therefore, not limited to the use of silver salts.

I have now disclosed the use of al-ginates in printing plates of three forms or typesfirst, as a coating ald-' hering to a support for use as a direct image printing plate; second as a light-sensitive plate using alginates with which bichrornate salts are incorporated; and third, as a photosensitive plate in which silver salts are incorporated.

I claim:

l. 'A planographic printing plate comprising a 'base sheet and a hydrophilic coating on the base sheet having an insolubilized alginate as the sole effective [hydrophilic colloid, an inert filler, and an image formed of an ink receptive, water repellent material anchored on the hydrophilic colloid coating.

2. A planographic printing plate comprising a base sheet and a hydrophilic lithographic surface on the base sheet having an insolubilized alginate as the sole effective hydrophilic colloid, an inert filler in finely divided form dispersed with the colloid in amounts ranging from one part by weight of colloid to 5 to 8 parts by weight filler, and an image formed of an ink receptive, water repellentvmaterial anchored on the hydrophilic colloid coating.

3. A lithographic printing plate comprising a paper base sheet and a continuous hydrophilic, lithographic coating on the surface of the base sheet having an insolubilized polyvalent metal salt of alginic acid as the effective colloid and in which the coating contains aninert filler in uniform distribution with the alginate and an image formed of an ink receptive, water repellent material anchored on the surface of the hydrophilic lithographic coating.

4. Alithographic printing plate comprising a paper base sheet and a continuous, hydrophilic, lithograhic coating on the surface of the base sheet having an in-.

so'lubilized polyvalent metal salt of alginic acid as the effective colloid and in which the coating contains an inert fil ler present in amounts ranging from 5-8 parts by weight of the filler to 1 part by weight of the alginate in unifom distribution throughout the coating, and an image fiormed of an ink receptive, water repellentmateri al anchored on the surface of the hydrophilic lithographic coating.

5. A lithographic printing plate comprising a paper base sheet and a continuous, hydrophilic, lithographic coating on the surface of the base sheet having the effective colloid fiormed of the reaction product of an alginate and a water soluble polyvaient metal salt in which the latter is present in an amount ranging from 0.5 to 5.0 percent by weight of the alginate and inert siliceous filler, and an image formed of an ink receptive, water repellent mraterial anchored on the hydrophilic lithographic coating.

References Cited in the file of this patent UNITED STATES PATENTS 349,760 Stanford Sept. 28, 1886 1,162,926 Ingham Dec. 7, 1915 1,361,783 Thornton Dec. 7, 1920 1,521,509 Dorel Dec. 30, 1924 1,759,956 Reed May 27, 1930 Structural Carbohydrate Chemistry (Percival). lished by Frederick Muller Dtd, 29 Great James Street,

OTHER REFERENCES W. C. 1, London, England, 1950, pages 158, 159, 1.60

and 161.

Copy in Scientific Library.

Pub- 

1. A PLANOGRAPHIC PRINTING PLATE COMPRISING A BASE SHEET AND A HYDROPHILIC COATING ON THE BASE SHEET HAVING AN INSOLUBILIZED ALGINATE AS THE SOLE EFECTIVE HYDROPHILIC COLLOID, AN INERT FILLER, AND AN IMAGE FORMED OF AN INK RECEPTIVE, WATER REPELLENT MATERIAL ANCHORED ON THE HYDROPHILIC COLLOID COATING. 